Processes known from the state of the art are described hereafter with reference to the known arrangement illustrated in FIG. 11. This arrangement has a means 11 for determining the control values, a means 12 for determining non-stationary transition values, a regulating means 13 and an internal-combustion engine 14 with a throttle flap 15, injection-valve arrangement 16 and pressure sensor 17 in the intake pipe 18 and with a lambda probe 19 in the exhaust pipe 20. It will initially be assumed that the internal-combustion engine 14 is being operated in a controlled manner. In this case, only the signal from the means 11 for determining the control values acts on the injection-valve arrangement 16. Values of operating parameters, especially the set angle of the throttle flap 15 and the engine speed, are fed to the means 11 for determining the control values, whereupon the means 11 emits an injection-time signal. It is also possible for only the pressure signal from the intake-pipe pressure sensor 17 to be fed as an input signal to the means 11 for determining the control values. The injection time is then set essentially in proportion to the measured pressure. For the full-clad range, the signal is advantageously also corrected by means of values which are read out from a family of characteristics as a function of values of operating parameters.
Simply controlling the-injection time is often insufficient for achieving a desired exhaust-gas quality. This can be improved with the aid of the lambda probe 19 and the regulating means 13. For this purpose, the lambda actual value from the lambda probe 19 is compared with a lambda desired value in a comparator stage 21, and the difference value is fed as a control deviation to the regulating means 13 which, as a function of the control deviation, determines a set value in the form of a regulating factor RF which, in a set-value logic stage 22, is multiplied by the value emitted by the means 11 for determining the control values. The control circuit described guarantees that control values by which the desired lambda value cannot be obtained alone are corrected in such a way that this object is nevertheless achieved.
Irrespective of whether the fuel quantity to be injected is merely controlled or whether there is a pilot control with superposed regulation, it must be remembered that the values emitted by the means 11 for determining the control values are normally determined for stationary operating states. However, if, for example, acceleration takes place between a first stationary operating state and a secondary stationary operating state, an acceleration enrichment is required in the meantime. So that this non-stationary situation according to the example or even other non-stationary situations can be dealt with, the means 12 for determining non-stationary transition values is provided. If values of operating parameters change with a high time gradient, the means 12 for determining non-stationary transition values emits a time sequence of values which are logically linked to control values in a non-stationary correction stage 23.
The non-stationary correction can be present on controlled systems or on pilot-controlled systems with superposed regulation. In all the practical applications, particular problems arise in those situations in which plurality of non-stationary conditions respectively initiating new non-stationary transition functions are satisfied in a short time sequence. This often leads, practice, to overlaps which reinforce or cancel one another in an undesirable way.
To prevent overlaps of this type, attempts are made to determine the control values permanently by the same process, that is to say not to differentiate between stationary or non-stationary operating states. Such a process is described in: `Non-stationary behavior--a factor in engine tuning` by M. Theissen, H.-St. Braun and G. Kramer in Conference Volume 1 Aachener Conference, Vehicle and Engine Technology '87, Aachen October 1987. The errors occurring in the determination of control values in non-stationary processes when no special measures are taken are designated as updating errors, phase errors and wall-film errors.
The updating error is dealt with in a conventional way, namely in that, when a non-stationary event has occurred after the calculation of the fuel quantity to be fed during the next stroke and the new fuel quantity taking this event into account can be taken into account before the conclusion of the intake stroke, an after-injection takes place.
The wall-film error is calculated individually as a function of the values of various operating parameters.
The phase error is an error which originates particularly from the fact that an air-quantity meter measures not only the air sucked in for combustion, but also the air serving for increasing the pressure in the intake pipe. This phase error is compensated by adapting the slope of the signal from the air-quantity meter to the slope of the intake-pipe pressure. The intake-pipe pressure is therefore measured, and the air mass sucked in for combustion during each stroke is determined by means of the intake-pipe pressure.
Because the phase error is adjusted by adapting the slope of the signal from the air-mass meter to the slope of the signal from the pressure sensor, in a non-stationary situation this process behaves in a similar way to those standard processes in which the air mass sucked in for combustion is determined directly from the measured intake-pipe pressure. However, it is a known fact in these processes that they do not compensate in a fully satisfactory way for the phase error which occurs during a non-stationary process.
The object on which the invention is based is to provide a process for determining the fuel quantity to be fed to an internal-combustion engine during each stroke, by means of which phase errors can largely be prevented.